This invention relates to a method and apparatus for stabilization of He.sub.2 (a.sup.3 .SIGMA..sub.u.sup.+) molecules in liquid (superfluid) helium for vacuum ultraviolet lasing.
The shorter wavelengths, increased resolution, and higher power densities of coherent radiation in the ultraviolet (UV) and vacuum UV regimes, as contrasted with optical wavelengths, are of great importance in applications, e.g., in physics and chemistry experiments (especially for molecular reaction studies), for power transmission in space, and in biomedical experiments and practice.
A vacuum UV laser using electronically-pumped superfluid helium has been proposed in U.S. Pat. No. 3,972,008 in which spatial periodicity in the liquid helium is induced by subjecting the fluid to acoustical or other energy, to establish standing waves. These standing waves produce resonant zones in the fluid, and the result is lasing in the wavelength regime around 0.0800.mu.m. One variation which has been proposed in the aforesaid patent applies a laser beam through a semitransparent mirror to induce periodicity in the fluid by photon energy instead of acoustic energy. The standing waves that demark the periodicity are thus produced by laser energy which in some multiple of the laser radiation that is to be generated by the system. In the present invention, optical pumping is not supplied for the purpose of inducing periodicity in the fluid, but rather to effect spin alignment of the He.sub.2 (a.sup.3 .SIGMA..sub.u.sup.+) molecules for the purpose of increasing their population concentration and lifetime by inhibiting their deexcitation in bimolecular collisions.